Telecommunication systems according to the 3GPP-standard offer high and variable bit-rates and are capable of providing new types of services to the users, involving real-time audio and video, still images and text, e.g. news, sport results and weather forecasts. By means of the High Speed Downlink Packet Access (HSDPA)-feature of the 3GPP-standard, the system capacity and the peak data rates are increased in the downlink direction, and the transfer delays are reduced. In order to be able to use the HSDPA service, the user must have a user equipment that is HSDPA capable, otherwise the user can only use DCH services provided by earlier releases of the standard.
In WCDMA systems, the dedicated channel (DCH) services according to an earlier release of the standard and the high speed downlink packet access (HSDPA, hereinafter referred to as HS) services can be run simultaneously in a same cell with a same carrier. For HS services, there could be a very large power fluctuation over HS time transmission intervals (TTIs), usually 2 ms which corresponds to three time slots. This is extremely true for the delay sensitive low bit-rate HS Guaranteed Bit-Rate (GBR) services because the data has to be scheduled in very bad channel conditions sometimes due to the tight delay requirements. For DCH services, the signal to interference ratio (SIR) target is adjusted by an outer loop power control (OLPC) in order to reach the block error rate (BLER) target, and the DCH power is adjusted by an inner loop power control (ILPC) in order to reach the SIR target. The ILPC combats the fast interference fluctuation. The OLPC combats the influence of the environment and user equipment (UE) mobility which can not be completely conquered by the ILPC. The OLPC execution period depends on the DCH TTI length.
Currently, there are two existing solutions to allocate the HS power. The first solution is that all the remaining power resource can be allocated as the available power resource for HS service. The second solution is to allocate a certain fixed available power for HS services. In this solution, there is a fixed amount of power resources reserved for HS services. The power interaction between HS and DCH services exists in these two solutions and this power interaction could be more serious in the first solution than in the second solution. This means that additional measures could be taken to handle such power interaction to improve the system performance.
For the first solution, the power interaction between HS and DCH service is shown FIG. 2, in which the HS power is denoted 20 and the DCH power 21. The total available power is denoted 22. The mean value of the HS power and the mean value of the DCH power are denoted 27 and 28 respectively. Also, in FIG. 2, the HS operation area is represented with 23 and the unused power is shown as 26. Suppose the DCH TTI, denoted with 25, is 20 ms, e.g. DCH Circuit switched (CS) speech, the OLPC execution period is 20 ms and the ILPC is performed once per slot. For HS service, both the HS-SCCH and HS-DSCH power are adjusted once per TTI, denoted with 24, i.e., 3 time slots. Though the ILPC frequency is higher than that of the HS-SCCH and HS-DSCH power adjustment, the ILPC could not effectively combat the interference peak in the first time slot of the HS TTI 24 when a sudden large HS power is allocated and sometimes could not be fast enough to combat the HS interference in the following 2 consecutive slots. That's because the sudden HS power increase (in dB) could be several times as the ILPC up step (in dB). This means that the probability of DCH block error occurring is much higher when a sudden high HS pulse (clear from FIG. 1) occurs than without such an HS power change. Because of the jump algorithm in the OLPC for DCH, when a data block for a UE is erroneous, the target SIR is increased in a large step (shown with small arrows pointing upwards), while when a block for the UE is right, the target SIR is decreased in a much smaller step (shown with small arrows pointing downwards). Even though such kind of high HS pulse may happen at a very low frequency, the OLPC adjusts the target SIR for DCH services to a relatively high level in order to reach the BLER target. Afterwards, for most HS TTIs 24 with very low HS Tx power, the SIR target for most DCH users is much higher than necessary, which is obviously a power waste.
For the second solution, besides the similar power interaction between HS and DCH service as in FIG. 2, there is another problem of low power utilization efficiency because the HS power limit does not change even though more power could be allocated for HS services when the situation with very high HS and very low DCH traffic load encountered or more power could be allocated for DCH services when the situation with very low HS and very high DCH traffic load encountered.